Can and must are modal auxiliary verbs. Can shows ability.

• She can speak several foreign languages.
• They are very rich. They can buy anything they want.
• You can come on Monday or Tuesday.
• She can solve any puzzle.
• He is very strong. He can easily beat any opponent.

We can use can to talk about possibility in questions and negative sentences.

• She left office at 6.30. She cannot be here before 7.30. (It is not possible for her to be here before 7.30.)
• ‘Who can it be?’ ‘That cannot be Peter. He is an France.’
• ‘Where can Susie have gone?’ ‘She cannot have gone to college. It is Sunday today.’

Must shows necessity and obligation.

• People must pay their taxes so that nations can prosper. (It is necessary for people to pay their taxes.)
• You must start arriving on time.
• I must find a new job.
• People must obey the laws.

Must not shows prohibition.

• You must not ignore your health.
• People must not break the laws.
• You must not be rude to your elders.
• You must not steal.
• You must not lie.

We can also use must to talk about a logical inference.

• There is no light in her room. She must be sleeping.
• It is already 10 o’clock. He must have reached home.

Fill in the blanks with can or must.

1. That is ridiculous. You ……………………….. be joking.

2. There is the doorbell. Who ……………………….. it be?

3. It ……………………….. be Susie. She is in Toronto. (can’t / mustn’t)

4. What ……………………… I do for you?

5. The refugees have already run out of food. They …………………………. be starving.

6. I am not free at the moment but I ……………………………. talk to you at lunchtime.

7. Indians ……………………………. visit Nepal without a visa.

8. We are going skiing on the weekend. That ………………………… be exciting.

9. If she left home at six, she …………………………. be here soon.

10. The doctor said that I ……………………………. lose weight.

11. …………………………. you see the bird on that branch?

12. …………………………. I talk to the manager?

Answers

1. must, 2. can, 3. can’t, 4. can, 5. must, 6. can, 7. can, 8. must, 9. must, 10. must, 11. can, 12. can

Worksheet 2

Fill in the blanks with must or can.

1. ……………… I help you?

2. …………….. I wait any longer?

3. …………….. I leave earlier today?

4. You …………………….. (not) go before you finish the job.

5. ……………… you lend me a few dollars?

6. Where ………………. I buy batteries?

7. How ……………… I get to the bus stand?

8. You ……………….. not park in front of a fire hydrant.

9. You ………………… listen to wise people.

10. You ……………… not leave young babies unattended.

Answers

1. can, 2. must, 3. can, 4. cannot / must not, 5. can, 6. can, 7. can, 8. must, 9. must, 10. must